Multiple user access channel

Abstract

A communications system may include a satellite and user equipment (UE) devices. When the UE devices have uplink (UL) packets to transmit, each UE device may randomly select a time slot within a finite time window associated with a time reference of the satellite. The UE device may identify a path length between itself and the satellite and may generate a timing advance based on the path length, the time reference, and the time slot. The satellite may begin to receive the UL packets within the time window and may search received signals over the time window to identify the UL packets. The satellite may recover data payloads from the identified UL packets and may pass the recovered data payloads up a protocol stack. By limiting the search to the time window, the satellite may correctly distinguish the UL packets while using a minimal amount of processing resources.

What is claimed is: 
     
       1. A method of operating a user equipment device to communicate with a terrestrial network via a communications satellite, the method comprising:
 identifying a path length between the electronic device and the communications satellite; 
 selecting a time slot from a finite time window for arrival of an uplink data packet at the communications satellite, wherein the uplink data packet comprises a data payload; 
 multiplying bits of the data payload by a user equipment access code; 
 appending the user equipment access code to the data payload; 
 generating a timing advance based on the selected time slot and the identified path length; and 
 transmitting, in a satellite communications band, the uplink data packet to the communications satellite based on the timing advance. 
 
     
     
       2. The method of  claim 1 , wherein identifying the path length comprises:
 identifying a location of the user equipment device on Earth; 
 identifying a location of the communications satellite in space from an almanac stored at the user equipment device; and 
 identifying the path length based on the identified location of the user equipment on Earth and the identified location of the communications satellite in space. 
 
     
     
       3. The method of  claim 1  further comprising:
 receiving a downlink (DL) beacon from the communications satellite; and 
 generating the timing advance based on a time reference identified by the DL beacon received from the communications satellite. 
 
     
     
       4. The method of  claim 1  wherein the finite time window has a duration between 0.1 ms and 10 ms and wherein selecting the time slot comprises randomly selecting the time slot from a plurality of time slots in the finite time window, further comprising:
 randomly selecting a frequency channel from a plurality of frequency channels in the satellite communications band, wherein transmitting the uplink data packet comprises transmitting the uplink data packet in the randomly selected frequency channel; 
 identifying a velocity of the communications satellite from an almanac stored at the user equipment device; 
 identifying a doppler shift based on the identified velocity; and 
 adjusting the randomly selected frequency channel to compensate for the identified doppler shift. 
 
     
     
       5. The method of  claim 1 , wherein the user equipment access code comprises a pseudorandom user equipment access code, the method further comprising:
 duplicating bits of the data payload by a spreading factor to produce a series of duplicated bits, wherein multiplying the bits of the data payload by the user equipment access code comprises multiplying the series of duplicated bits by the pseudorandom user equipment access code. 
 
     
     
       6. The method of  claim 1 , wherein the multiplied bits of the data payload correspond to bits of the data payload that are duplicated by a spreading factor. 
     
     
       7. The method of  claim 1 , wherein the satellite communications band comprises a band selected from the group consisting of:
 a C band, an S band, an L band, an X band, a W band, a V band, a K band, a K a  band, and a K u  band. 
 
     
     
       8. A method of operating a user equipment device to communicate with a terrestrial network via a communications satellite, the method comprising:
 identifying a path length between the electronic device and the communications satellite; 
 selecting a time slot from a finite time window for arrival of an uplink data packet at the communications satellite, wherein the uplink data packet comprises a data payload; 
 multiplying bits of the data payload by a user equipment access code; 
 generating a timing advance based on the selected time slot and the identified path length; 
 transmitting, in a satellite communications band, the uplink data packet to the communications satellite based on the timing advance; and 
 adjusting the timing advance to compensate for relativistic time dilation between the user equipment device and the communications satellite. 
 
     
     
       9. The method of  claim 8 , further comprising:
 appending the user equipment access code to the data payload. 
 
     
     
       10. The method of  claim 8 , further comprising:
 receiving a downlink (DL) beacon from the communications satellite; and 
 generating the timing advance based on a time reference identified by the DL beacon received from the communications satellite. 
 
     
     
       11. The method of  claim 8 , wherein the multiplied bits of the data payload correspond to bits of the data payload that are duplicated by a spreading factor. 
     
     
       12. The method of  claim 8 , wherein the user equipment access code comprises a pseudorandom user equipment access code. 
     
     
       13. A method of operating a communications network having a communications satellite to communicate with user equipment devices on Earth, the method comprising:
 receiving, during a finite time window and in a satellite communications band, radio-frequency signals at the communications satellite that include time-advanced uplink signals transmitted by the user equipment devices; 
 searching, over frequency and the finite time window, the radio-frequency signals to identify the time-advanced uplink signals transmitted by the user equipment devices, wherein searching the radio-frequency signals comprises correlating the radio-frequency signals with a user equipment access code; and 
 recovering data payloads of the identified time-advanced uplink signals transmitted by the user equipment devices, wherein recovering the data payloads comprises multiplying bits from one of the identified time-advanced uplink signals by the user equipment access code to recover duplicated bits. 
 
     
     
       14. The method of  claim 13 , further comprising:
 forwarding the radio-frequency signals from the communications satellite to the gateway, wherein searching the radio-frequency signals comprises searching the radio-frequency signals at the gateway. 
 
     
     
       15. The method of  claim 13 , further comprising:
 with the communications satellite, transmitting a downlink beacon that identifies a reference time of the communications satellite prior to the finite time window. 
 
     
     
       16. The method of  claim 13 , wherein the time-advanced uplink signals transmitted by the user equipment devices arrive within different respective time slots of the finite time window. 
     
     
       17. The method of  claim 13 , wherein the finite time window has a duration between 0.5 and 10.0 ms. 
     
     
       18. The method of  claim 13 , wherein correlating the radio-frequency signals produces correlated data and searching the radio-frequency signals further comprises:
 converting the correlated data from a time domain to a frequency domain to produce frequency domain correlated data; 
 filtering the frequency domain correlated data to produce potential time-advanced uplink signals; 
 attempting to decode the potential time-advanced uplink signals; and 
 discarding potential time-advanced uplink signals that are unsuccessfully decoded, wherein recovering the data payloads comprises recovering the data payloads from the potential time-advanced uplink signals that are successfully decoded. 
 
     
     
       19. The method of  claim 13 , wherein recovering the data payloads comprises:
 averaging the duplicated bits based on a spreading factor to produce average values; and 
 rounding the average values to the closer of 1 or 0. 
 
     
     
       20. The method of  claim 13 , wherein recovering the data payloads further comprises:
 averaging the duplicated bits based on a spreading factor to produce average values.